Constant velocity joints are common components in automotive vehicles. Typically, constant velocity joints are employed where transmission of a constant velocity rotary motion is desired or required. Common types of constant velocity joints are a plunging tripod, a fixed tripod, a plunging ball joint and a fixed ball joint. These types of joints currently are used in front wheel drive vehicles, or rear wheel drive vehicles, and on the propeller shafts found in rear wheel drive, all wheel drive and four wheel drive vehicles. These constant velocity joints are generally grease lubricated for life and sealed by the use of sealing boots when used on drive shafts. Thus, constant velocity joints are sealed in order to retain grease inside the joint while keeping contaminants and foreign matter, such as dirt and water, out of the joint. To achieve this protection, the constant velocity joint is usually enclosed at the open end of the outer race by a sealing boot made of a rubber, thermoplastic, or silicone material. The opposite end of the outer race generally is enclosed by a dome or cap, known as a grease cap in the case of a disk type joint. A monoblock or integral stem and race design style does not use a grease cap, but is sealed by the internal geometry of the outer race. This sealing and protection of the constant velocity joint is necessary because contamination of the inner chamber may cause internal damage and destruction of the joint. Furthermore, once the inner chamber of the joint is lubricated, it is lubricated for life.
During operation, the constant velocity joint creates internal pressures in the inner chamber of the joint. These pressures have to be vented to the outer atmosphere in order to prevent pressure build-up which occurs during operation of the joint and which may destroy the boot. If the pressure build-up is allowed to reach a critical state, the boot, protecting the joint from contaminants and water, may crack and deteriorate, or blow out, thus losing its sealing capability. Generally speaking, a constant velocity joint is usually vented by placing a small hole generally in the center of the grease cap or at least one hole around the outer periphery of the outer race. These prior methods of venting the gas are sometimes not adequate because if the constant velocity joint is in a static state and not rotating the lubricating grease may settle in the vent hole and block or hinder its function of venting any internal gas pressure. In addition, the vent hole may become blocked by the lubricating grease while the constant velocity joint is rotating or in a dynamic state. Furthermore, the lubricating grease may be purged or excreted into the external environment if the grease communicates with the vent hole. This type of vent hole may also allow the infiltration of contaminants. If the vent hole becomes blocked, the internal pressure may build up causing the joint seal to fail due to a ruptured boot or other catastrophe. Furthermore, the constant velocity joint, after running for long periods of time, creates very high temperatures along with high pressures which are vented through the current vent holes. However, if the constant velocity joint is submerged, splashed, or saturated in water or other contaminants, the water will, via vacuum caused by the temperature differential or by gravity, be sucked into the constant velocity joint chamber, thus contaminating the grease lubricant and reducing the life of the constant velocity joint. Therefore, the ingress of water and other contaminants and egress of joint grease through the vent hole may reduce the life expectancy for the constant velocity joints.
Therefore, there is a need in the art for a constant velocity joint vent valve that will prevent the build up of internal gas pressure while eliminating the ingress of contaminants and preventing the egress of joint grease, and provide a vent pathway that is not subject to plugging or occlusion by the joint grease. There is also an additional need to have a constant velocity joint vent valve that, upon pressure differential reversal, will diffuse or permeate air back into the constant velocity joint chamber while keeping external contaminants out of the joint.